review classifier: run on ACP when the swarm settings choose it

The swarm settings gain `runtime` (`api-key`, the default, or `acp`) and
an `acp` provider record: an https base URL, the provider's model, and
its prices per million tokens. A PUT now changes only the fields its
body names, so the settings form that sends model, effort and limit
leaves the runtime alone; `null` clears `effort` or `acp`. The body stays
strict, and the stored document keeps #5192's lenient read.

The controller sends the runtime in each run request. On `acp` the
classifier runs one prompt on a new `opencode acp` session per
classification through hive-runtime's AcpRuntime, in a scratch
directory, with a config rendered from the settings. opencode runs
`read` and other tools without asking, so OPENCODE_PERMISSION
{"*":"deny"} takes every tool away from the model, and a deny-all policy
refuses any request on top. The title call, which resends the prompt,
is turned off. The deadline cancels the turn, and a turn that does not
end within 15s of that is dropped, which also covers an agent stuck
before its prompt. The answer is the final assistant text, as ACP has
no result event.

The provider key is read per run from
swarm/services/review-classifier/acp-provider, which the bao UI's
admins login may create and update, and reaches opencode through
AcpRuntime::with_provider_key and the trampoline's allowlist.

Each ACP classification's cost is computed from the configured prices
and the reported tokens, and added to
hyperhive.review_classifier.cost.usage labelled repo, pr, model and
currency.

Part of #5096

nix/host-modules/swarm-bao.nix

@@ -604,14 +604,19 @@ let
   # to fetch config repos.
   builderForgeTokenLeaf = "swarm/services/builder/forge/token";
 
+  # The review classifier's ACP provider key, the nix half of
+  # `swarm_secret_client::review_classifier::acp_provider_key_path`. Written
+  # and read like the API key above.
+  classifierAcpKeyLeaf = "swarm/services/review-classifier/acp-provider";
+
   # The UI's OIDC client secret. The publisher writes it; the granter reads it
   # into the `oidc` auth method's config, which is the only copy bao uses.
   baoUiClientLeaf = "swarm/services/${cfg.ui.oidc.clientId}/oidc/client";
 
   # What an OIDC login through the UI gets: the key tree and each key's KV
-  # metadata, and a write on the one leaf the operator fills by hand. Never a
-  # value: KV v2 serves values under `data/`, and the one `data/` stanza has
-  # no `read`. The UI needs no `sys/` grant on top:
+  # metadata, and a write on the leaves the operator fills by hand. Never a
+  # value: KV v2 serves values under `data/`, and no `data/` stanza has a
+  # `read`. The UI needs no `sys/` grant on top:
   # `sys/internal/ui/mounts` lists any mount the token holds a capability
   # under, and the rest it calls is in the `default` policy.
   operatorViewerPolicyName = "swarm-operator-viewer";
@@ -622,6 +627,9 @@ let
     path "${credentialMountPath}/data/${classifierApiKeyLeaf}" {
       capabilities = ["create", "update"]
     }
+    path "${credentialMountPath}/data/${classifierAcpKeyLeaf}" {
+      capabilities = ["create", "update"]
+    }
   '';
 
   # authelia's operator group (`operatorGroup` in ./swarm-authelia.nix, the
@@ -1001,15 +1009,17 @@ let
     }
   ];
 
-  # The review classifier: the API key the operator writes, read once per run,
-  # and its own queue client secret, read at start. Both by the daemon inside
-  # its container.
+  # The review classifier: the API key and the ACP provider key the operator
+  # writes, the one its run's runtime needs read once per run, and its own
+  # queue client secret, read at start. All by the daemon inside its
+  # container.
   reviewClassifierReaders = [
     {
       name = "swarm-review-classifier";
       cn = baoDeploy.reviewClassifierCommonName;
       policyText =
         readStanza "${credentialMountPath}/data/${classifierApiKeyLeaf}"
+        + readStanza "${credentialMountPath}/data/${classifierAcpKeyLeaf}"
         + readStanza "${credentialMountPath}/data/swarm/services/${hyperhiveCfg.swarm.review-classifier.clientId}/oidc/client";
     }
   ];
@@ -1868,9 +1878,10 @@ in
       description = ''
         Subject the store's `swarm-review-classifier` cert-auth role accepts:
         the identity the review classifier presents from inside its
-        container. Its grant is two paths, read only:
-        `swarm/services/review-classifier/anthropic-api-key` and its own
-        queue client secret.
+        container. Its grant is three paths, read only:
+        `swarm/services/review-classifier/anthropic-api-key`,
+        `swarm/services/review-classifier/acp-provider` and its own queue
+        client secret.
 
         ⚠️ Reserved as a hive name by ./swarm.nix, like its siblings.
       '';